1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light (herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays and gamma-rays).
2. Description of the Prior Art
Photoconductive materials constituting photoconductive layers for solid state image pick-up devices, electrophotographic image forming members in the field of image formation, or manuscript reading devices, are required to have a high sensitivity, a high SN ratio [Photocurrent (I.sub.p)/Dark current (I.sub.d)], spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. In particular, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon (hereinafter referred to as a-Si) has recently attracted attention as a photoconductive material. For example, German Laid-Open Patent Publication Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and German Laid-Open Patent Publication No. 2933411 an application of a-Si for use in an electro-photoconverting reading device.
However, under the present situation, the photoconductive members having photoconductive layers constituted of conventional a-Si are further required to be improved in the overall characteristics including electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light, etc., and environmental characteristics during use, and further stability with lapse of time and durability.
For instance, when applied in an image forming member for electrophotography, at the dark portion, injection of charges from the support side cannot sufficiently be impeded; the image forming member employed is not free from some problems with respect to dielectric strength or durability against repeated continuous uses; or there occurred image defects commonly called as "black area" on the images transferred on a transfer paper which may be considered to be due to the local discharge destroying phenomenon, or so called image defects commonly called as "white line", which may be considered to be caused by, for example, scraping with a blade employed for cleaning. Also, when used in a highly humid atmosphere or immediately after being left to stand in a highly humid atmosphere for a long time, so called "unfocused image" was frequently observed in images obtained.
Further, when the layer thickness is as thick as ten and some microns or higher, there tend to occur such phenomena as loosening or peeling of layers off from the support surface or formation of cracks in the layers with lapse of time when left to stand after taking out from a vacuum deposition chamber for layer formation. These phenomenon will occur particularly frequently when the support is a drum-shaped support conventionally employed in the field of electrophotography. Thus, there are problems to be solved with respect to stability with lapse of time.
Thus, it is required in designing of a photoconductive material to make efforts to solve all of the problems as mentioned above along with the improvement in characteristics of a-Si materials per se.
In view of the above points, the present invention is achieved as a result of extensive studies made comprehensively from the standpoints of applicability and utility of a-Si as a photoconductive member for image forming members for electrophotography, solid state image pick-up devices, reading devices, etc. Now, a photoconductive member having a photoconductive layer which comprises an amorphous material containing at least one of hydrogen atom (H) and halogen atom (X) in a matrix of silicon atoms [hereinafter referred to comprehensively as a-Si (H,X)], so called hydrogenated amorphous silicon, halogenated amorphous silicon or halogen-containing hydrogenated amorphous silicon, which photoconductive member is prepared by designing so as to have a specific layer structure, is found to exhibit not only practically extremely excellent characteristics but also surpass the photoconductive members of the prior art in substantially all respects, especially markedly excellent characteristics as a photoconductive member for electrophotography. The present invention is based on such finding.